BIOELECTRICITY GENERATION POTENTIAL OF SELECTED AGROWASTES USING MCROBIAL ELECTROCHEMICAL REACTOR

Abstract

Microbial electrochemical reactor is a novel bioelectrochemical system (BES) with the potential of generating electrical energy from bulk biomass/organic waste through microbial metabolism. This study determined the bioelectricity generation potential of maize husk, sweet potato peels, wheat shaft and sugar cane shaft; all obtained from different agricultural waste sites within Akure South Local Government Area of Ondo state Nigeria. Microorganisms associated with the agrowaste substrates were isolated, characterised and identified using conventional/classical and molecular methods. The proximate, mineral, vitamin, ethanol, organic acid and enzyme contents of the agrowastes were determined before and after fermentation with standard techniques. Dual chamber microbial fuel cells (MFCs) were constructed for each substrate from where voltage and current readings were evaluated over 21 days. Physicochemical parameters were evaluated at intervals over fermentation period. Microbial community in each MFC set up were also identified at the end of fermentation using standard methods. Microorganisms isolated were screened for enzyme production and microorganisms with highest frequency of occurrence were further studied. The study showed a total of 17 bacteria, 11 moulds and 4 yeasts were isolated from samples and the MFC electrodes. These included; Acinetobacter baumanii, Staphylococcus aureus, S. epidermidis, Micrococcus luteus, Bacillus subtilis, B. cereus, B.licheniformis, B. megaterium, B. anthracis, Paenibacillus dendritiformis, Lactobacillus plantarum, Proteus mirabilis, Corynebacterium spp, Escherichia coli, Klebsiella spp, Pseudomonas aeruginosa, Xanthomonas campestris, Enterococcus faecalis, Alternaria alternata, Fusaium solani, Aspergillus niger, Neurospora crassa, Aspergillus flavus, Penicillium chrysogenum, Microsporum canis, Aspergilus terreus, Fusarim oxysporum, Rhizopus stolonifer, Trichophyton mentagrophytes, Saccharomyces crevisiae, Candida albicans, Rhodotorula glutinis and Geotrichum candidum. Proximate analysis showed that the moisture content of the raw agrowastes ranged between 0.71 and 3.03% but increased significantly (P<0.05) after fermentation with values ranging between 18.71 and 38.77%. Ash content reduced after fermentation, while the protein and fat content increased after fermentation. Fibre and carbohydrate content of the agrowastes also reduced significantly (P<0.05) after fermentation. Potassium and iron content of all the agrowastes increased after the fermentation process. Sodium content of potato peels and maize husk reduced after fermentation, while the sodium content of sugar cane shaft as well as wheat shaft increased after fermentation process. Vitamin assay showed that all the agrowastes were rich in vitamin A and C, which increased after the fermentation process. Organic acids content of all the samples increased after fermentation. All the agrowastes used as substrate in this study were good sources for enzyme production (Cellulase, Protease, Pectinase, Amylase). The findings from the microbial fuel cells set up showed that Maize husk recorded the highest voltage and current (with peak values of 80mV and 80uA respectively) as compared to the other agrowastes. Higher microbial load was recorded at the anode compared to the cathode electrode for all the agrowaste substrates of the MFC set up. Bacillus cereus, Bacillus subtilis, Bacillus megaterium and Bacillus licheniformis that were isolated from this study screened positive to amylase, protease, cellulase and pectinase production. The findings from the proximate, mineral and vitamin evaluation of samples revealed that fermentation greatly enriched the protein, minerals and vitamin contents of the agrowastes, hence it can be recommended as good supplement in compounding animal feed provided that it is acceptable and highly digestible. In conclusion, the study showed that the agrowastes demonstrated potential for bioelectricity generation and can be used as suitable substrates in the microbial fuel cell for bioelectricity production.